Humans, livestock and rat monocrotaline (MCT) pneumotoxicity is associated with a spectrum of pulmonary vascular lesions reminiscent of idiopathic pulmonary hypertension in humans. A feature common to all forms of pulmonary hypertension is that the initial insult leads to progressive vascular remodeling, which underlies sustained, irreversible increases in pulmonary arterial pressure. Studies in our laboratories demonstrate that the polyamines have a central role in the MCT-caused pathogenic vascular structural remodeling. The major objective of this proposal is to determine cellular and molecular mechanisms by which polyamines mediate MCT-generated signals that initiate and drive inappropriate structural remodeling processes in pulmonary vessels. SMC hypertrophy and increased synthesis and accumulation of collagen and elastin clearly contribute to the increased thickness of hypertensive pulmonary arteries. To assess mechanisms by which polyamines mediate MCT-induced elastin and collagen gene expression, the specific target cell(s) and temporal relationship of MCT-induced inappropriate regulation of ODC elastin and specific collagen gene expression will be identified; and the impact of depletion of cellular polyamine contents on the MCT-enhanced elastin, collagen and ODC gene expression will be determined. The contents of whole lung and intrapulmonary artery mRNAs an protein for elastin, the collagens I, II, & III, and ODC from MCT-treated and control rats will be quantitated. The impact of depletion of polyamine content upon elastin and collagen expression will be tested. In situ hybridization will be employed to determine ODC, elastin and collagen gene expression and modulation at the individual cell level. Molecular mechanisms by which MCT alters ODC gene expression will be explored. Smooth muscle and fibroblast cells will be isolated from rat pulmonary arteries to determine if stable phenotypic alterations in elastin, collagen or ODC are produced by MCT-treatment and if polyamine depletion can prevent phenotypic alterations. One key question relates to the intracellular mechanisms which couple MCT pneumotoxicity to cellular changes underlying structural remodeling. Therefore, the ability of lung cell from MCT-treated rats to generate factors that cause polyamine-dependent alterations in vascular growth and production of collagen and elastin will be examined.